The present invention relates to an apparatus for cooling hot rolled steel rod in direct sequence with a rod mill and, more particularly, to an apparatus which cools steel either by forced convection or by actually supplying heat to produce a retarded cooling rate during transformation of the steel. Cooling while supplying heat is defined as exposing the steel to radiant heat or to a fluid medium which is substantially above room temperature. The medium can even be at the same temperature as the rod, or slightly higher to offset the loss of heat of the rod by radiation.
A process is known from U.S. Pat. No. 3,231,432 which cools hot rolled steel rod by forced air convection as the rod leaves the last stand of a rod mill. In the cited process, the rod is first formed into flat overlapping non-concentric rings. The rings are then conveyed into a cooling chamber. In the cooling chamber forced air contacts the rings and uniformly cools them. The cited process imparts good properties of tensile strength and ductility to most medium to high plain carbon steels. For a majority of finished products, such rod need not be heat treated subsequently. Additionally, in the cited process, scale loss is minimized.
However, when low carbon steels and certain steel alloys are cooled by the cited process, in some cases they may have inadequate ductility. This results from the fact that the cooling rate during transformation of the steel is too high. In fact, it is often difficult to keep the cooling rate low enough for such steels because the loss of heat by radiation is a major factor in the 500.degree.C to 700.degree.C (transformation) range. Although cooling in the open by natural convention alone is slower than forced (cold) air convection, it is much too fast for the necessary slow cooling for certain steels. Even an insulated box can absorb the radiated heat at a faster rate than may be tolerated by some steels. Accordingly, it is necessary in such cases to apply radiant heat or a heating cooling medium to the rod and to the chamber surrounding the rod so as to reduce the radiation heat loss rate.
During retarded cooling in air, however, the formation of scale is increased and thereafter, when the apparatus is again used for accelerated cooling, the residue of scale which cracks off and falls into the cooling chamber becomes a serious problem. If this accumulated scale is not removed, it will subsequently be blown into the atmosphere by the cooling blowers after a shift to normal high speed cooling, and scale blown around a mill may be a hazard to personnel as well as cause damage to equipment through contamination of lubricants.
There are several previously known methods for the general prevention or removal of scale. For instance, the use of a non-oxidizing or reducing atmosphere to prevent scale formation has been employed in furnaces. Using a reducing atmosphere, however, becomes complicated and difficult when the apparatus or a part of it is to be used for cooling by forced convection. In addition, after scale has already formed on the steel, there are conventional ways to remove it either by chemical or mechanical action. However, none of such conventional approaches deals with the problem of removing an accumulation of scale in apparatus which is adapted both for rapid cooling by forced air convection and for slow cooling under conditions where heat is added. The provision of equipment for so doing is one of the objectives of this invention.